The invention is related to Internet protocol (IP) telephony systems that allow users to place and receive telephone calls, and to send and receive text and video messages via data packets that are communicated over a data network.
A mobile telephony device conducts a voice over Internet protocol (VOIP) telephone call by linking itself to a data network using a wireless data connection. The wireless data connection could be a link to a wireless router that is coupled to a data network, such as a WiFi or WiMax router. Alternatively, a mobile telephony device could establish a wireless data connection to a data network over a data channel provided by a cellular telephony service provider.
If a mobile telephony device is conducting a VOIP telephone call, and the user of the mobile telephony device moves out of communication range of the wireless router or cell tower that the mobile telephony device has used to establish a wireless data connection, the call will be disconnected. However, it is also possible that the movement of the mobile telephony device will bring the mobile telephony device within communication range of a new wireless router or cell tower at the same time, or before, the mobile telephony device passes out of communication range of the first wireless router or cell tower. If this occurs, it would be desirable for the mobile telephony device to automatically establish a new wireless data connection with the new wireless router or cell tower, and for the call to continue through the new wireless data connection.
Unfortunately, it is difficult to transition a VOIP telephone call from a first wireless data connection to a second wireless data connection mid-call. During a VOIP telephone call, the mobile telephony device is sending data packets to and receiving data packets from a specific server, gateway or media relay in the data network. During call setup, the server, gateway or media relay will have been provided with the Internet protocol (IP) address and port number that data packets must be sent to in order to arrive at the mobile telephony device. Likewise, the server, gateway or media relay will expect to receive all data packets sent from the mobile telephony device from that same IP address and port number during the entire telephony session.
If the mobile telephony device transitions from a first wireless data connection to a second wireless data connection, the IP address and port number associated therewith are both likely to change. The mobile telephony device will still have the IP address and port number of the server, gateway or media relay that it has been communicating with, but it will be sending data packets bearing the media of the call to the server, gateway or media relay from its new IP address and port number. These data packets will not be recognized by the server, gateway or media relay as coming from the proper location. As a result, the data packets will be ignored. Likewise, the server, gateway or media relay will not know to re-direct data packets intended for the mobile telephony device to the new IP address and port number now being used by the mobile telephony device to continue the telephony session. For these reasons, it is difficult, or impossible, for a mobile telephony device conducting a VOIP telephone call to transition from a first wireless data connection to a second wireless data connection mid-call.